cottonwood water & sanitation districtseptember 2002 arber indirect potable reuse at cottonwood...

Cottonwood Water & Sanitation District September 2002

Arber

Indirect Potable Reuse at Cottonwood Water and Sanitation

District

Rick Arber, Ben JohnsonRichard P. Arber Associates

Pat MulhernMRE


ArberTypes of Reuse


ArberAgricultural & Industrial

• Exchanges• Recycle-process, cooling


ArberMunicipal

• Urban Landscape Irrigation• Indirect Potable Use• Direct Potable Reuse


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WTP

WWTP

AWT

Non-Potable Reuse


ArberUnplanned Indirect Potable

Reuse

WTP

WWTP

WTP

WWTP


ArberPlanned Indirect Potable Reuse

WTP WWTP

AWT

Aquifer


ArberDirect Potable Reuse

WTP

WWTP

AWT


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Cottonwood Water and Sanitation District


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CWSD….• Formed in 1981• 1200 Acres of residential

and commercial development

• Slow development in 1980s• Rapid development in 1990s


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• Water Supplies• Deep wells (Dawson, Denver,

Arapahoe, Laramie Fox Hills)• Cherry Creek alluvium

• Wastewater • ACWWA Lone Tree Creek WWTP


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• Deep Wells– 995 acre Feet

– Fe, Mn, H2S

• Alluvial Water– 141 acre feet senior rights– 585 acre feet junior rights– Upstream discharges (Pinery,

Parker, Stonegate)


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• Deep Wells – non-renewing– draw down/capacities– require treatment

• Alluvial Wells– renewable– high capacity– require treatment


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CWSD SAFETY FACTOR DEMAND AND AVERAGE YEAR SUPPLY vs. TIME

* Includes 20% Additional Safety Factor Above Projected Demand

0

500

1000

1500

2000

2500

3000

1995 2000 2005 2010 2015 2020

Year

Dem

and/

Supp

ly (A

F/YR

)

YearlyDemand *

AverageYear Supply

Linear(YearlyDemand *)


ArberAlternatives

• Deep Wells– Non-renewing; eventual

depletion– Additional wells need with

draw down– Limited production– Treatment required


ArberAlternatives

• Dual Distribution $$$• Import Groundwater $$$


ArberAlternatives

• ReuseRenewable supplyExtend deep groundwater Greater production


ArberCentralized vs. Decentralized

Treatment

• Capital cost 10% less for centralized treatment.

• O&M cost similar for centralized treatment and decentralized.

• Centralized treatment easier to operate.


ArberThe Plan


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• Average daily demand 2 mgd

• Maximum daily demand 6 mgd


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ArberTreatment

• Cartridge Filters• UV?• Anti-scalant• Nanofiltration• Degassifier• pH adjust• Alkalinity• Chlorine


Arber Indirect Potable Reuse

• Multiple Barriers– WWTP/AWT– Alluvium (3000 ft.,~

1.5 years travel)– Membrane water

treatment (100%)– Final disinfection


ArberConcentrate Disposal

• Cherry Creek Basin– PO4

• Split Flow– ACWWA WWTP (base flow)– Irrigation


ArberPilot Testing


Arber Objectives

• Evaluate effectiveness of NF on raw water

• Determine design criteria• Evaluate fouling potential• Evaluate feed, permeate, and

concentrate water quality• Select appropriate membrane


ArberPilot Testing Plan

• Three month duration– Test different membranes

• Sample water quality 6 times– At beginning and end of each

membrane test• Operate at 83% recovery

– 2.0 gpm permeate– 0.5 gpm concentrate


Arber Performance

• Tested two membranes– Osmonics– Filmtec (2 month test)

• Added anti-scalant chemical(Pro Treat)– Potential for sulfate precipitation

reduced

• No significant fouling was observed


ArberResults

• Both membranes performed well– Osmonics tighter - higher driving pressure– Filmtec looser - lower contaminant rejection

• Average Rejection– TDS

• Osmonics 68% Filmtec 62%– Hardness

• Osmonics 84% Filmtec 69%– TOC successfully rejected by both

membranes (BDL)


ArberProject Costs

• Treatment– $9.3 million

• Ancillary facilities– $2.3 million


Arber Public Education Program

• Consultant• Literature• CDPHE involvement• Public meetings


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• Predesign underway• Design 2003• Construct 2004• Start up 2005

Schedule


ArberConclusions

• NF effective in removing TOC

• Multiple barriers provide public health protection

• Indirect potable reuse is viable, cost effective water supply for CWSD

• Public support is needed


Arber

• Questions?

cottonwood water & sanitation districtseptember 2002 arber indirect potable reuse at cottonwood...

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